Disk drive using various kinds of disks, such as optical disks, magneto-optical disks, flexible magnetic-recording disks and similar disks for data-storage are in the art. In particular, hard disk drives (HDDs) have been widely used as data-storage devices that have proven to be indispensable for contemporary computer systems. Moreover, HDDs have found widespread application to motion picture recording and reproducing apparatuses, car navigation systems, cellular phones, and similar devices, in addition to the computers, because of their outstanding information-storage characteristics.
An HDD includes a magnetic-recording disk and a head-slider; data on the magnetic-recording disk is read and written with the head-slider. To increase recording capacity per unit area on the magnetic-recording disk, the areal density of magnetically recorded information is increased. However, reduction in recording bit length may not cause an increase in areal density because of thermal fluctuation in magnetization of the medium. Generally, influence by the thermal fluctuation will increase as the value of KuV/kT is smaller, where Ku is a magnetic anisotropy constant of the magnetic-recording medium, V is a minimum volume of a unit of magnetization, for example, magnetic grain size, k is Boltzmann's constant, and T is absolute temperature. Accordingly, to increase areal density Ku, or alternatively, V, are made greater so as to reduce the influence of the thermal fluctuation.
To address this issue, a perpendicular magnetic-recording (PMR) method has been developed that records magnetic signals perpendicularly onto a double-layered PMR medium having a soft-magnetic underlayer with a probe-pole write element. This method may apply a stronger recording magnetic field to the magnetic-recording medium. Therefore, a magnetic-recording recording layer of a magnetic-recording disk with a large magnetic anisotropy constant, Ku, may be used. Moreover, in a magnetic-recording disk in the PMR method, increase in V may be achieved by growing magnetic particles in the film thickness direction while maintaining the magnetic particle diameter on the magnetic-recording medium surface small, or maintaining the bit length small.
Magnetic-recording disks used in an HDD have multiple concentric data tracks and servo tracks provided. Each servo track includes servo data sectors containing address information. Each data track also includes a plurality of recorded data sectors containing user data. Between servo sectors provided discretely in the circumferential direction, data sectors are recorded. A magnetic-recording head of a head-slider, which is supported by a rotary actuator, accesses a selected data sector in accordance with address information contained in the servo data, and writes data to the data sector, or alternatively, reads data from the data sector.
To increase the recording density of a magnetic-recording disk, the spacing between a magnetic-recording head flying in proximity to the recording surface of the magnetic-recording disk and the magnetic-recording disk, as well as variations in the spacing, are reduced. One technique to control the spacing provides a heater in a head-slider; the heater heats the magnetic-recording head to adjust the spacing, which is referred to herein by the term of art, “thermal fly-height control” (TFC). TFC applies current to the heater to generate heat, causing protrusion of the magnetic-recording head by thermal expansion. This reduces the spacing between the magnetic-recording disk and the magnetic-recording head. Scientists and engineers engaged in HDD design, manufacturing and development are interested in controlling the reduction in spacing to meet the ever increasing demands for reliability and performance from the HDD market.